1. Field of the Invention
The invention concerns a holding arrangement for a winding enclosure which is subject to external forces and is fastened within a vacuum tank by means of tie rods, and in which an electric winding cooled to a low temperature is arranged.
2. Description of the Prior Art
Electric windings, particularly superconducting windings, which are cooled to a low temperature by means of a cryogenic medium, must generally be heat-insulated against their environment. They are, therefore, arranged in a winding enclosure and are, advantageously, surrounded by a vacuum within a vacuum tank. Additionally, reflecting wrinkled foil, so-called superinsulation, may also be provided between the winding enclosure and the vacuum tank for reducing the heat influx into the cooled winding. Such heat insulation, however, can transmit only very small forces in the transversal direction. For this reason, additional holding means for the enclosure are usually provided so that the excited winding maintains its position within the vacuum tank under the action of external forces. Such forces can occur between the winding and the vacuum tank if for example, several windings are excited asymmetrically or if a winding is rotated.
In German Patent No. 1,514,633, a holding device for a thermally insulated and superconducting winding is taught in which the device is arranged inside the winding enclosure. The winding enclosure, in turn, is held within an outer housing by tie rods. Each tie rod is provided with an elastic intermediate member whose spring excursion is chosen so that upon cooling the superconducting winding from room temperature to a temperature near absolute zero, the length and position changes of the tie rods due to thermal effects are substantially compensated for without stressing the tie rods. Moreover, by limiting the spring excursion of the elastic intermediate member, which may, for example, be a cup spring, the effect of the intermediate member can be substantially eliminated at the low temperature required to bring about superconduction. The forces acting on the winding are then transmitted only by the tie rods.
For limiting the spring excursion of the elastic intermediate member of the above device, an adjusting device situated outside the outer housing is required. If this outer housing is to serve as the vacuum housing, the required feedthroughs for the adjusting device must be designed so as to be vacuum-tight. The design of such feedthroughs is, therefore, quite expensive. In addition, the feedthroughs are required to have a relatively large cross section, so that, in general, they result in heat conduction losses which must be compensated for by providing special cooling for the superconducting winding.
It is an object of the present invention to simplify and improve the aforesaid holding arrangement. In particular, it is an object of the present invention to modify such arrangement so that the winding enclosure is safely and firmly secured at all temperatures and under the action of alternating external forces, without the need for additional adjusting devices and in a manner which minimizes the heat influx into the winding.